In the folder PSP_GAME\USRDIR\ in the GTA UMD there is a folder called...are you ready..."LUASCRIPTS". Don't believe me? Go check. I thought Sony was AGAINST homebrew...I guess they saw some potential in the Lua Scripting.
BTW, I saw this while viewing the UMD through FileAssistant with the TIFF eLoader. I thought Fanjita said that he couldn't get UMD access through the eLoader because it was kernal mode.